1. Field of the Invention
The present invention relates to a deflection yoke for a Braun tube, and more particularly, to a ferrite core in a RAC type deflection yoke employed for improving a deflection sensitivity of a Braun tube.
2. Background of the Related Art
In general, a color Braun tube is provided with an in-line type electron gun, in which a self-converging type deflection yoke with a non-uniform magnetic field is employed for converging three electron beams onto one dot on a fluorescent film as red(R), green(G), and blue(B) electron beams are emitted arranged on a horizontal line in parallel. Referring to FIGS. 1xcx9c2B, a related art color cathode ray tube, and a RAC type deflection yoke applied thereto will be explained.
Referring to FIG. 1, the related art color cathode ray tube is provided with a panel 1 forming a front surface thereof, a fluorescent film 3 on an inside surface of the panel 1 having a coat of red(R), green(G), and blue(B) fluorescent materials applied thereon, a shadow mask 2 in rear of the fluorescent film 3 for selection of colors of the electron beams incident to the fluorescent film 3, a funnel 6 welded to a rear of the panel 1, an electron gun 5 fitted inside of a neck part in a rear portion of the funnel 6 for emission of electron beams 7, and a RAC type deflection yoke 4 mounted to surround an outer circumference of the neck part in the rear portion of the funnel 6 for deflection of the electron beams emitted from the electron gun in a horizontal or vertical direction.
And, referring to FIGS. 2A and 2B, the RAC type deflection yoke 4 is provided with one pair of horizontal deflection coils 41 for deflecting the electron beams emitted from the electron gun 5 in the cathode ray tube in a horizontal direction, one pair of vertical deflection coils 42 for deflecting the electron beams in a vertical direction, a ferrite core 44 for reducing losses of magnetic forces generated by currents in the horizontal deflection coil 41 and the vertical deflection coil 42 to enhance a deflection efficiency, a holder 43 for fixing relative positions of the horizontal deflection coils 41, the vertical deflection coils 42, and the ferrite core 44, physically holding and fastening the same, and insulating between the horizontal deflection coils 41 and the vertical deflection coils 42 and fastening the horizontal deflection coils 41 and the vertical deflection coils 42 to the cathode ray tube, a COMA free coil 45 mostly fitted to a neck side of the holder 43 for improving a coma aberration generated by a vertical barrel type magnetic field, a ring band 46 fitted to a neck side of the holder 43 for fastening the cathode ray tube and the deflection yokes 4 physically, and magnets 47 fitted to an opening side of the deflection yokes for correction of raster distortion of a picture.
In the meantime, referring to FIGS. 3xcx9c4C, the rectangular ferrite core in the related art RAC type deflection yoke, and the vertical deflection coils fastened to the ferrite core will be explained in detail. FIG. 3 illustrates a perspective view of the rectangular ferrite core in FIG. 2A.
Referring to FIG. 3, the related art ferrite core 44 is provided with, when the related art ferrite core 44 is compared to the cathode ray tube, a small sized neck portion 44c identical to the neck part of the cathode ray tube, an opening portion 44a large sized compared to the neck portion 44c identical to a screen side of the cathode ray tube, and an intermediate portion 44b, an intermediate region of the neck portion 44c and the opening portion 44a. Particularly, the ferrite core has a section circular at the neck portion 44c, which gradually becomes non-circular as the section goes from the neck portion 44c to the opening portion 44a which is rectangular. That is, the intermediate portion 44b is a region of transition from a circle to a rectangle, and dashed lines in the intermediate portion 44b in FIG. 3 indicate a point P where the transition from a circle to a rectangle starts.
FIG. 4A illustrates a perspective view of the vertical deflection coils in FIG. 2A, FIG. 4B illustrates a front view of FIG. 4A, and FIG. 4C illustrates a side view of FIG. 4A.
Referring to FIGS. 4Axcx9c4C, the vertical deflection coils 42 are disposed on an inside of the rectangular ferrite core 44 and has a contour substantially similar to the foregoing ferrite core. That is, identical to the rectangular ferrite core 44, the vertical deflection coils 42 also has a small sized neck portion 42c substantially similar to the neck part of the cathode ray tube, a large sized opening portion 42a substantially similar to a screen side form of the cathode ray tube, and an intermediate portion 42b which is an intermediate region of the neck portion 42c and the opening portion 42a. And, the vertical deflection coils 42 collectively have a section circular at the neck portion 42c, which gradually becomes non-circular as the section goes from the neck portion 42c to the opening portion 42a which is rectangular. That is, the vertical deflection coils 42 also have a point P of transition from a circle to a rectangle and the intermediate portion 42b, a region of transition from a circle to a rectangle starting from the point of transition.
In the meantime, the regions of transition from a circle to a rectangle of the rectangular ferrite core 44 and the vertical deflection coils 42 have a ratio of transition from a circle to a rectangle which becomes the greater as the region goes from the neck portion to the opening portion. The ratio of transition from a circle to a rectangle is defined as follows.
Referring to FIG. 6, a circle is drawn centered on a corner of a square which has a length HL in a horizontal direction axis xe2x80x98Hxe2x80x99 and a length VL in a vertical direction axis xe2x80x98Vxe2x80x99, taking a diagonal line as a radius xe2x80x98Rxe2x80x99. And, )H is defined as a difference between the radius R and the horizontal side length of the square HL, and )V is defined as a difference between the radius R and the vertical side length of the square VL. And, a sum of )H and )V is defined as )HV, i.e., )HV=)H+)V, and the ratio of transition(transition ratio) from a circle to a rectangle is defined to be )HV/R. In a case of a true circle, when both )H and )V are xe2x80x9c0xe2x80x9d, the transition ratio is xe2x80x9c0xe2x80x9d, and in a case of a square, the transition ratio is approx. 0.6.
The operation of the aforementioned RAC type deflection yoke 4 will be explained.
In general, the horizontal deflection coils 41 have currents with a frequency equal to 15.75 KHz or over applied thereto, for deflecting the electron beams in the cathode ray tube in a horizontal direction by using a magnetic field formed as the currents are applied thereto. And, in general the vertical deflection coils 42 have currents with a 60 Hz frequency applied thereto, for deflecting the electron beams in a vertical direction by using a magnetic field formed as the currents are applied thereto. In the meantime, recently, self-convergence type deflection yokes are developed mostly, which permits convergence of the three electron beams on a screen by using a non-uniform magnetic field formed by the horizontal deflection coil 41 and the vertical deflection coil 42, without using any additional circuits or devices, separately. That is, distributions of wounds of the horizontal deflection coils 41 and the vertical deflection coils 42 are adjusted, such that magnetic fields at respective portions(the opening portion, the intermediate portion, and the neck portion) are a barrel form or a pin-cushion form, for exerting different deflection forces to the three electron beams depending on positions of the three electron beams so as to converge the three electron beams which have different distances from starting points to arrival points onto the same point. Moreover, in the case of magnetic field formation by applying the currents to the horizontal deflection coils 41 and the vertical deflection coils 42, since the deflection of the electron beams throughout the entire surface of the screen only by using the horizontal deflection coils 41 and the vertical deflection coils 42 is not adequate, the ferrite core 44 of a high magnetic permeability is used for minimizing a loss a magnetic force in a returning path of the magnetic flux, to enhance an efficiency of the magnetic field, and, thereby enhancing a magnetic force.
And, referring to FIGS. 5A and 5B, the horizontal deflection coils 41 have an upper and a lower coils 41U and 41L connected in parallel, to which a horizontal deflection current of a saw tooth wave form is applied for forming a horizontal deflection magnetic field of a pin-cushion type so as to deflect the three electron beams (i.e., red, green, and blue electron beams) emitted from the electron gun 5 in a horizontal direction, as the force exerting on the electron beam by the horizontal deflection magnetic field is inversely proportional to a third power of a distance between an inside surface of the horizontal deflection coil and the electron beam according to the Flemming""s left-hand rule. The RAC type deflection yoke 4 can improve a deflection sensitivity compared to a circular deflection yoke in the related art because both the rectangular deflection coils 41 and 42 and the ferrite core 44 lead the distance to the electron beams to be closer than the circular deflection yoke. That is, the rectangular deflection coils 41 and 42 and the ferrite core 44 in the deflection yoke lead the distance from the electron beams to the deflection coils closer by approx. 20% compared to the circular deflection yoke in the related art, the rectangular deflection coils 41 and 42 and the ferrite core 44 have approx. 20xcx9c30% improved horizontal and vertical deflection sensitivities.
However, the foregoing rectangular ferrite core has a formation error in a level of ∀2% because a percentage of contraction of the material reaches to as much as 20%. Particularly, the rectangular ferrite core formed to improve the sensitivity of the deflection yoke 4 results in a greater formation error. That is, since the rectangular ferrite core should be formed to have different length and width, and a circular neck portion 44c and a rectangular opening portion 44a with a transitory intermediate portion 44b, an error in grinding the ferrite core becomes more than three times at the maximum compared to the circular core in the related art. The rectangular ferrite core with the regions of transition from a circle to a rectangle in the related art has a difficulty in managing dimensions accurately as the grinding of the transition region is difficult, that results in a production yield of the rectangular core no more than 50% of the circular ferrite core, with a unit cost approx. 200% higher than the circular ferrite core.
Accordingly, the present invention is directed to a deflection yoke for a cathode ray tube that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a deflection yoke for a cathode ray tube, which can maintain advantages of the rectangular ferrite core of improving a deflection sensitivity as they are, but permits an easy inside surface grinding and improves distribution of an inside dimension.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the deflection yoke for a cathode ray tube includes horizontal deflection coils and vertical deflection coils for deflecting electron beams emitted from an electron gun in a horizontal or vertical direction, a ferrite core for reducing a loss of a magnetic force generated at the horizontal and vertical deflection coils to enhance a magnetic efficiency, and a holder for fixing the horizontal deflection coils and the vertical deflection coils and the ferrite core to preset positions, and insulating between the horizontal deflection coils and the vertical deflection coils, wherein the ferrite core includes a main ferrite core with a curved surface and supplementary ferrite cores each with a planar surface fitted to the main ferrite core.
The main ferrite core includes planar surfaces on an opening portion side of the main ferrite core for fitting the supplementary ferrite core a top portion and a bottom portion of the main ferrite core.
The planar surface is formed starting from the opening portion toward the neck portion direction, at a ratio of a length of the planar surface to an entire length of the main ferrite core in an axis direction of the cathode ray tube being 5%xcx9c70%.
The planar surface started from the opening portion toward the neck portion direction is formed such that an angle between a line connecting an inner front edge of the opening portion which has an arc form and a center of the opening portion of the main ferrite core and a horizontal line passed through the center of the opening portion is 20Excx9c80E when the main ferrite core is seen from a screen side.
The angle between the line connecting an inner front edge of the opening portion which has an arc form and a center of the opening portion of the main ferrite core and a horizontal line passed through the center of the opening portion is preferably 36.7E.
Of an entire length of the main ferrite core in an axis direction of the cathode ray tube the planar surface is formed starting from points in front of points on an outer circumference of the main ferrite core onto which the region the transition from a circle to a rectangle of the vertical deflection coils starts are projected.
Particularly, of an entire length of the main ferrite core in an axis direction of the cathode ray tube, the planar surface is formed starting from points in front of points on an outer circumference of the main ferrite core onto which points of the vertical deflection coils of which transition ratio are 0.3 are projected.
The planar surface in the main ferrite core is formed in parallel to the axis of the cathode ray tube, or sloped at an angle to the axis of the cathode ray tube.
A section of the main ferrite core in parallel to a surface of the opening at any point of the axis of the cathode ray tube has concentric circles or arcs.
The supplementary ferrite core is a plate with a thickness having a width which becomes the smaller as it goes the farther from the opening portion side toward the neck portion side of the main ferrite core, or a rectangular in a plan view.
The supplementary ferrite core is a plate with a thickness having a width which becomes the smaller as it goes the farther from the opening portion side toward the neck portion side of the main ferrite core, to be semicircular or trapezoidal in a plan view.
The supplementary ferrite core includes a step for fitting to the planar surface of the main ferrite core.
The step includes at least one portion formed to be fit to the planar surface of the main ferrite core, and a height formed the lower as it goes the farther to a rear portion.
The planar surface is formed by sintering a substantially conic main ferrite core and cutting off top and bottom portions of the sintered conic main ferrite core, or by sintering the main ferrite core directly without any additional cutting off process.
A front surface of the opening portion of the main ferrite core and a front surface of the supplementary ferrite core are aligned to the same vertical plane.
The front surface of the supplementary ferrite core is positioned at a point in rear of the front surface of the opening portion of the main ferrite core in an axis direction of the cathode ray tube, if the planar surface is sloped with respect to an axis of the cathode ray tube.
The deflection yoke further includes a supplementary holder having a through hole for inserting front portions of the opening portion of the main ferrite core and the supplementary ferrite cores, thereby receiving and holding the front portions of the opening portion of the main ferrite core and the supplementary ferrite cores.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.